The Heart River irrigation project, in southwestern North Dakota, lies in the Missouri Plateau section of the Great Plains physiographic province, which extends from the Missouri escarpment to and beyond the western border of the State. The area ranges in altitude from 1,620 to 2,275 feet and locally has strong relief.
The floor of the Heart River Valley is underlain by alluvial deposits of Quaternary age. In the westernmost part of the areas the Fort Union formation of Paleocene (Tertiary) age forms the valley sides, but in a downstream direction the Cannonball and Ludlow formations, here undifferentiated, also of Paleocene age, crop out in the valley sides and underlie progressively broader areas of the upland surface. The Hell Creek formation of Upper Cretaceous age appears above stream level only in the stretch of the valley between the center of T. 136 N., R. 85 W., and the northeastern part of T.. 137 N., R. 84 W. Glacial Drift, which once covered the whole area, now has been almost entirely removed by erosion except for .scattered boulders on the uplands. The Cannonball and Ludlow unit and the Fort Union formation yield, moderate supplies of ground water, and the river alluvium yields more abundant supplies. At the present rate of withdrawal and with normal precipitation there is little danger of seriously depleting the supply. In 1946 the average depth to water in observation wells in the Heart River Valley was 19 feet, whereas the depth to water in observation wells in the upland averaged 30 feet.
The Dickinson area is small and is about 45 miles upstream from the Heart River irrigation project. Ground-water levels in the Dickinson municipal well field have declined considerably within recent years, but the impounding of Heart River water is expected to insure a more adequate water supply for the town.
Samples of ground water from four wells in the lower Heart River Valley were analyzed to determine the present mineral character of the waters in this region. Waters from shallow and deep wells in the Dickinson area were analyzed to assist in determining the practicability of further utilization of ground water as a public supply. A map showing areas of the least-mineralized ground water in the Dickinson area is presented and the need of further exploratory work is discussed.
